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Audi follows a two-pronged approach this year at the Le Mans 24 Hours and in the newly created FIA World Endurance Championship (WEC) – the 2012 model Audi R18 exists with and without hybrid drive. The trick: the base of both cars is completely identical, which is why the additional logistical effort could be reduced for Audi Sport and Audi Sport Team Joest.

When Audi Sport designed the R18 TDI for Le Mans 2011 the technicians focused from the very beginning of the ‘R18’ project on a compact 3.7 liter V6 TDI with innovative architecture and equipped with a mono-turbocharger.

Exactly this now pays dividends: the engine requires very little installation space, is light and plays its role in compensating for the hybrid system’s additional weight. In spite of the latest restrictions imposed by the Automobile Club de l’Ouest (ACO) Audi Sport still extracts over 375kW (510 hp) and a maximum torque exceeding 850 Nm from the power unit thanks to the efficiency of the overall concept.

At first glance the R18 ultra does not look much different to last year’s Le Mans winning R18 TDI. However, under the guidance of Head of Technology Dr. Martin Mühlmeier the Audi Sport engineers have done a great job and left hardly a single area of the car untouched. The result is a largely new LMP1 prototype – including a modified carbon-fiber monocoque, which continues to excel through its one piece construction.

“To compensate for the weight the subject of lightweight design and construction was the focus throughout the entire car,” says Christopher Reinke, Technical Project Leader LMP at Audi Sport. “We have systematically and logically pursued ultra lightweight design and construction without compromising the aspects of safety and reliability. The same applies to the monocoque just as it does for the engine, gearbox and other components.” Almost every component in the V6 TDI engine was completely reworked and adapted to suit the new regulations, which targeted a reduction in engine power of around seven percent and which was achieved in the form of a smaller engine air intake restrictor (45.8 instead of 47.4mm diameter) and a reduction in the maximum boost pressure from 3.0 to 2.8bar. In addition, the fuel cell volume was reduced from 65 to 60 liters and even 58 liters for a diesel hybrid.

There is a genuine innovation in the area of the transmission: a new carbon-fiber composite gearbox housing was developed for the R18 – a premiere in endurance racing. Innovative materials and manufacturing processes to reduce mass are also used in the suspension area. The electromechanical steering, which gives the drivers even more precise feedback, is completely new.

The extremely advanced aerodynamic configuration from 2011 was initially adapted to suit the new regulations that, as an example, stipulate openings above the wheel arches. Additionally, the product concept catalogue also specified a further significant reduction in aerodynamic drag despite the increased cooling requirements for the hybrid components. Vision out of the closed cockpit was also improved through detailed optimization. The engineers also improved the windshield cleaning and the area illuminated by the full LED headlights. Fundamentally, the hybrid drive, in combination with the quattro four-wheel drive, results in an extension of the front section of the monocoque. However, it also has positive effects on the overall balance of the conventionally powered twin brother, which more than lives up to its model name ‘R18 ultra:’ it is the lightest Le Mans Prototype that Audi Sport has ever built. Accordingly the engineers can position the additional ballast weight exactly where it is required for the races – even if both cars have exactly the same overall weight, namely 900 kilograms stipulated by the LMP1 car regulations.

E-tron Quattro hybridThe Audi R18 e-tron quattro is the first Audi race car no longer accelerated exclusively by a combustion engine. With the R18 e-tron quattro Vorsprung durch Technik means the development of an independent hybrid system including complete networking, control, software, algorithms and interfaces. As in other areas Audi Sport also cooperates with external manufacturers during the manufacture of components for the hybrid system. Development partner for the accumulator is Williams WHP, for the Motor Generator Unit (MGU) long-standing technology partner Bosch. The system integrated into the front axle is comprised of two driveshafts, the Motor Generator Unit including planetary gears, an electronic flywheel accumulator, an insulation monitoring unit for high voltage safety and the control system.
The process of energy recuperation is explained relatively easily, the technical implementation is, in contrast, extremely challenging. The recuperation of energy occurs during braking. In the process, the wheels drive the MGU. The braking zones permitted are defined by the regulations. The Motor Generator Unit electrically accelerates a carbon-fiber flywheel that runs in a highvacuum. After the corner is taken and the driver accelerates again the system delivers the energy to the front axle above a speed of 120km/h. The regulations allow 500kJ of energy to be transferred to the front wheels between two braking phases. The planetary gears adapt the transmission ratio during acceleration and braking. The two independently powered axles on the e-tron quattro are synchronized exclusively via electronic control strategies. This control occurs automatically without driver intervention. The entire charging process (recuperation) is controlled by two parameters: the braking process and the accumulator’s state of charge. The energy emission process (boost) is defined by the minimum speed of 120km/h stipulated by the regulations, the race strategy selected, the throttle pedal movement and acceleration of the car. Location and number of hybrid phases per lap are defined for every circuit by the FIA.

The flywheel is housed in the passenger seat area of the cockpit which has been redesigned to improve visibility, with the side windows enlarged and the head restraints reworked.

“The greatest challenge was to find the ideal compromise,” reasons Wolfgang Appel, Head of Vehicle Development at Audi Sport. “It was a question of perfectly balancing weight, performance, hybrid concept, regulation constraints and the packaging – the distribution of all the components in such a way that no appreciable disadvantages arise in the conventional vehicle since both cars are absolutely identical, with the exception of the hybrid system, in design and construction.”
There are some minor differences between the two cars including around the nose duct, there is a small interchangeable panel on the outside edge of the duct (above), which is probably related to cooling the brakes, and in the case of the hybrid possibly the e-motor, although that is liquid cooled via a radiator in the left sidepod. On the hybrid (below) the shape of the duct is different an d the aperture slightly larger.
The front driveshaft of the R18 hybrid means that a hole is required in the front of the chassis. This is present on both the hybrid and the combustion car though on the latter a blanking plate is used. Ballast is placed in the void left by the absent electric motor. See below with the drive shaft fitted.
The R18 tub has a large dimple on its roof, this allows cleaner airflow to the V6 engine. See below.
On the rear wing there are some very interesting features including this serrated gurney, with a number of V shapes cut into the edge (below), these only appear on the outer edge and likely have some role in dealing with the dirty air from the front and rear wheels.
Around the rear end there are a lot of very interesting details, the grooves around the rear wheel hole are to prevent the dirty air from the wheel arch area spilling into the crucial area ahead of the rear wing.
The R18 chassis have slightly different numbers depending on whether the car is in hybrid or combustion specification. R18-X-205 as seen below is a combustion car, if it was a hybrid the chassis number would be R18-H-205, or in other words x is for combustion and h is for hybrid.

2013 Updates
In 2013 a heavily revised R18 made its debut at Sebring, immediately obvious were its Toyota TS030 style rear wing extensions, which exploit a loophole in the regulations covering wheel arches.
These extensions in theory increase downforce. When the Audi LMP project was launched in 1999, the rear wing was allowed to fill a maximum volume of 2,000 mm (width) x 400 mm (length) x 150 mm (height). Today, these dimensions have been reduced to 1,600 x 250 x 150 mm. The wheel arch extensions allow the wing to extend beyond that.
Through a large number of individual solutions, such as the rear wing swan necks it claims to have compensated for a major part of the lost downforce. It allows significantly improved airflow to the wing.

One innovation introduced at Sebring certainly increases downforce, an exhaust blown diffuser. On the updated car the exhaust is split downstream of the single turbocharger, the tail pipes are now rerouted to the rear wheel arches. On the 2012 R18 there was a single exit at the rear of the car (below).
Rerouting the exhausts is not a straight forward task and probably lead to some packaging compromises but the Audi engineers believed that the performance gain was worth it. The regulations strictly limit where openings can appear in the cars bodywork, but there is some freedom in the wheel arch. Which is where the R18 exits can be found (below)
This approach is the same concept used by Formula 1 teams since 2009. The exhaust gasses are channelled in such a way that they block a vortex from the base of the rotating tyre from entering the diffuser. If the vortex enters the diffuser then it reduces its effectiveness, and in turn total vehicle downforce. This relies on the exhaust gas having a significant mass flow rate, something that you may not expect with a turbo diesel engine with particulate filters. But it seems that there is enough.
The F1 teams would run thier engines at around 100% throttle all of the time in order to get the maximum mass flow, with the accelerator pedal acting as a torque demand switch. This off throttle running made a distinctive rasping sound and the open throttle running increased fuel consumption by up to 10%. It is not clear if the Audi engine is set up to run off throttle in this way or if it is run normally. The current breed of F1 cars are not permitted to run off throttle, but still feature blown diffusers (using the Coanda effect to rout the gasses to the right area). It could be that the Audi engineers have taken this approach, though it can make the car incredibly tricky to drive as when the driver lifts off the throttle or runs at part throttle there is a significant drop in downforce and a change in the cars overall balance, which then changes again when the driver applies the throttle.

Spa update
Two versions of the R18 were run at Spa. Two cars ran in Sebring specification (above) whilst the third car was fitted with a long tail body (below).
This longer rear section is focussed on drag reduction.
Another area of drag reduction is the heat exchanger on the 2013 R18 which consists of what Audi calls an ‘innovative micro-tube radiator’. The conventional aluminum louver-finned radiator that creates high aerodynamic drag has been replaced by a system made up of more than 11,000 small tubes per radiator, and the radiators no longer require fins.
These radiators can be freely configured. With the same radiator size, the pressure drop of the airflow can be reduced by more than 25 percent. Alternatively, with pressure conditions remaining the same, the size of the radiator can be reduced accordingly.
A new front splitter was also introduced at Spa on the longtail car (above) compare it with the version run on the short tail cars (below)
The rear wing of the R18 also underwent major revision on the longtail car. The new foil was mounted lower and had a lower angle.
Compared to the short tail car (below) it is visually very different, likely the work of testing in the Sauber wind tunnel.

Le Mans
At the Le Mans test day four R18’s took part the three cars that would contest the race and a mystery fourth car running all in black. As of the 2014 season, a fundamentally new set of regulations will apply to sports prototypes. The new elements include a clearly reduced tire size. The smaller dimension corresponds to the current tire dimension for LMP2 sports cars (14 instead of 16 inches overall width, 28 instead of 28.5 inches outer diameter).

The aim for the black car according to an Audi Sport press release is to successfully manage this change, which marks the most radical one in the LMP1 class to date, while ensuring maximum safety under permanent loads. Therefore, Audi is making a race car equipped with measuring technology available exclusively for tyre testing on the test day. Aside from the racing event, this day provides the only opportunity during the year to use the circuit at Le Mans, as the tradition-steeped track primarily consists of public roads. The engineers are already in the process of simulating the aerodynamic effects and the axle loads to be expected with LMP1 race cars in 2014. Thus, the fourth R18 e-tron quattro will be running in a corresponding configuration in realistic conditions at the beginning of June.
“Our objective is to generate a database for handling the future tyres that is as versatile and reliable as possible,” emphasizes Head of Audi Motorsport Dr. Wolfgang Ullrich. “The tyres are an absolutely safety-relevant topic. The impending technological change is fundamental. Therefore, we are providing all the data being gathered to our long-standing partner Michelin as well. Ultimately, all Michelin partner teams will benefit from this. We thank the ACO and the FIA and WEC officials who paved the way for us to nominate a fourth car. This marks a commitment to high safety in racing.”
All four of the cars on the face of it were running the longtail bodywork first seen at Spa but there were some key differences, which suggests that the black car was testing more than just tyres.
This additional duct was fitted to the number four car, Christophe Reinke claims that it is not for the compressed air hybrid system tested earlier in the year but outlawed by the ACO, but merely for cooling. Cooling what though Reinke would not be drawn on (not the air hybrid though Reinke insists).
Of interest was the no.3 R18 which seemed to perform differently to its supposedly identical sister cars. It seemed to be able to run a lap longer than the other and it had a higher top speed. This suggests that it may have been running a lower drag level but there is no obvious sign of this on the cars bodywork. Another thoery rumoured before the race was that one car was running with either a different specification blown diffuser or possibly without one at all. This may account for the cars lower fuel consumption but perhaps not its higher top speed.
Audi driver Oliver Jarvis told Radio Le Mans reporter Shay Adam that the car was in the same specfication as the other two. We do not believe him. Jarvis has done much development work for the Audi team and tends to get the updated cars first.

Digital Editor / Deputy Editor
Sam grew up in South London within sight of the long abandoned Crystal Palace Race Circuit, yet found himself on work experience in the loom shop at Williams F1 aged 16. He has been heavily involved in the sport ever since, having gained a Nationa Diploma in Motorsport Engineering from East Surrey College (where he also built and raced a Group N Ford Fiesta) and studied Automotive Engineering at Oxford Brookes University.
Collins has written for Motorsport News, Autosport, Model Collector, Speed TV, 750 Bulletin, Rafahiya and a number of others. He has also written a number of books including Autodrome, and Unraced. He is also the Editor of Stockcar Engineering magazine.
As a driver Collins has competed in stockcar racing, Formula Vee, stage and road rallying as well as many local events. He still competes occasionally in the European Late Model Series. His fairly random musings on motorsport can be found on the official twitter feed @racecarengineer